Hub units for bearings with tapered raceways for rollers suitable for heavy loads are provided with one or two inner rings fitted onto an axle and outer rings mounted in the hub of the wheel. The inner rings have to be retained and preloaded so as to support the axial forces resulting from the inclinations of the raceways.
It is known to provide retaining end caps at the end of the axle, wherein the retaining end caps are fixed by means of three or four screws for preloading and retaining the bearing unit on the axle.
Retaining end caps in hub units of this type have to act as springs and thus allow for a predetermined flexibility in the axial direction. The strength and material properties, in particular the elastic properties of the ring are therefore highly relevant for the product as a whole and are extensively studied in advance using finite-element analysis algorithms. This problem has led to the technical prejudice that the end cap should be constituted by one massive single body made of strong and flexible steel and that protuberances or recesses should be avoided as far as possible.
Further, it is known to provide bearings other than the above tapered roller bearings with sensor units attached to the outer or inner ring. Typical sensor units are formed as temperature sensors, rotation sensor or vibration sensors suitable for detecting an operating status of the bearing, which may help to detect problems or wear at a very early stage.
Hitherto, sensor units as described above have not been used in railway hubs because it was considered impossible to integrate the sensor in such a way that the resulting assembly is sufficiently robust for operating the harsh conditions e.g. under freight trains.
A further difficulty is the provision of a sufficiently robust power supply for the sensor unit and a reliable possibility for reading out data.